With the above-mentioned appliances, various washing and/or drying cycles are carried out which are controlled by a programmer and which must almost always use water or air heated to a predetermined temperature.
Because the thermal energy produced by means of electric resistances has proved substantially more expensive than that produced by means of the burner of a central heating system, there are various appliances in the prior art which, for the washing operation, draw water from the central hot-water system and mix it by means of a mixer with a required quantity of cold water before introducing it into the appliance, generally at the bottom of same, so that the different types of cycle can be carried out. The programmer controls the operation of the mixer so as to arrive at the temperatures indicated for the various cycles.
However nowadays this type of operation has various disadvantages.
The first of these is that the water, once introduced into the electric domestic appliance, gradually cools on contact with the appliance and the articles to be washed or dried, and therefore, in order to be efficient, the cycle must have a duration relative to the average temperature which the water will have during said cycle, for which reason such duration will be appreciably greater than that which would be required for a cycle during which the water maintained a constant temperature.